The present invention concerns an apparatus for assembling the electron-emissive part of a cathode comprising a porous base metal penetrated with an electron-emissive material and a thin metal plate for covering the base metal.
Conventionally, the cathode used for a Braun tube, camera tube, etc. comprises a porous base metal penetrated with an electron-emissive material, a sleeve for mounting said base metal on one end thereof, and hereafter received by said sleeve. Referring to FIG. 1, the reference numerals 1, 2, and 3 respectively indicate the porous base metal penetrated with an electron-emissive material, the sleeve, and the thin metal plate that covers the base metal 1 in the form of a cup-shaped separating wall. The wall is welded or soldered to the sleeve at contact position 4, and the porous base metal 1 is soldered to the thin metal plate at contact position 5. The heater is not shown in FIG. 1.
The sleeve 2 is conventionally made of heat-durable metal to endure the operating temperature of the cathode which is generally greater than 1000.degree. C. The heater usually comprises a tungsten wire which is coated with alumina to secure insulation at a high temperature.
In operation, when the cathode is heated to a temperature above approximately 1000.degree. C., the Ba compound contained in the porous base metal 1 is emitted to the tungsten wire, attacking the insulating alumina thereon, so that the insulation of the heater is deteriorated, thereby consuming the heater. The heat-durable thin metal plate 3 is to keep the Ba compound from reaching the heater.
Referring to FIG. 2, the conventional apparatus for assembling the metal plate 3 and the porous base metal 1 presses the base metal 1 on the thin metal plate 3 by means of part A. Then, the porous base metal 1 and the thin metal plate 3 are pushed into the opening of die C for the metal plate 3 to cover the base metal 1. Thereafter part B is moved so that the edge portions of the thin metal plate 3 may be attached to the edge portions of the upper end of the base metal 1. Thus, the base metal is firmly fixed to the metal plate. In this case, the metal plate portion covering the side of the base metal is creased so as to reduce the contacting surface between the sleeve 2 and itself. Hence, the thermal conductance from the heater to the base metal is reduced. Namely, since there exist a number of gaps between the sleeve 2 and the separating wall, the emission current density is lowered due to the lowering of thermal efficiency.
Furthermore, the conventional apparatus intermittently operates to produce the electron emissive part, and therefore, has a low production efficiency.